1. Field of the Invention
The present invention relates generally to exposure units for controllably exposing light sensitive photographic materials to a light source. More particularly, the invention concerns a top loading, vacuum exposure unit for exposing photostencil materials to a source of light.
2. Discussion of the Invention
Several types of exposure units for exposing photostencil materials have been developed in the past. Typically these units comprise a light box having a glass top superimposed over a series of fluorescent lights. Mounted over the light box is a vacuum frame which includes a flexible mat that can be tightly drawn over the stencil by a vacuum pump so that the stencil is pressed firmly against the glass top of the exposure unit. Exemplary of prior art exposure units are those sold by McLogan Supply Co., Inc., of Los Angeles, California and by Screen Process Equipment Company of Atlanta, Georgia.
As a general rule in the prior art exposure units, the vacuum pump, which operates the vacuum frame, is typically mounted within the light box either below or to one side of the bay of fluorescent lights. A connector hose usually passes through the rear wall of the light box and interconnects the inlet of the vacuum pump and the outlet port of the vacuum frame. When the vacuum pump is energized, air is drawn from between the flexible mat and the stencil and through the hollow tubular sides of the vacuum frame to the inlet of the vacuum pump. With this construction, continuous operation of the vacuum pump causes the light box to become extremely hot making the unit difficult to work with and causing rapid degradation of the operating components of the unit. Further, because the vacuum hose typically extends from the back of the unit, the exposure unit cannot be located against a wall, but must be inconviently spaced apart from the wall a substantial distance. This results in lost floor space and exposes the vacuum hose to potential damage if the unit is accidentally pushed against the wall.
It is these drawbacks of the prior art units, namely the overheating problem caused by the improperly designed vacuum system, which the present invention uniquely overcomes. As will be discussed in greater detail hereinafter, the apparatus of the present invention embodies a vacuum pump having a thru-flow vacuum motor which continuously draws outside air through the vacuum frame causing substantial cooling rather than undesirable heating of the light box. The vacuum pump is interconnected directly with the vacuum frame by means of a novel direct connection so that no external connector hose is required. This enables the unit to be located against a wall and effectively prevents damage to the vacuum system. Additionally, the apparatus of the present invention includes a unique light-tight base which supports the light box and vacuum frame and provides safe and convenient storage for light sensitive materials. The base is also of a unique design allowing efficient ventilation of the storage compartment while maintaining the light-tight integrity thereof.